Shorepower short - help diagnose?

[kchace]

The "smart plug" system is expensive and found nowhere.

If a boat only needs 30A 120 onboard , by installing a 50A 120 plug and inlet socket on the existing cord it would be safe and parts , if required , found easily.

Any overload would be at the power pole end , so not endanger the boat.

I was thinking of doing just this the next time I have to replace a plug. Using the superior 50A plug/socket gives a good margin when used on a 30A line.

Ken

 

[Riverguy]

Dear all;

I was out on overnight winter cruise this week when a bad evening surprise hit me. Nordic Tug 32 2008. When I plugged into another marina's shore power and switched on - my entire shore power cord started smoking and smoke coming into the interior. Immediately unhooked from shore power and smoke cleared. The shore breaker never tripped but the shore outlet was badly charred on the ground terminal as was my shore power inlet on the boat. The entire shore power cord is burned in a helical pattern (see photos).

Next day opened up the boat to find the main power cable from the power inlet to the main 110V board is also burned (see photos) all the way the the 110V box; where I can follow the individual wires. Only the green (ground) wire is charred up to the main ground terminal.

Anyone up for telling me what could cause this? Any why no breakers stopped it from happening?
Thanks -

I'm late to the thread, but I have recently completed ABYC E-11 training (on top of that I have worked as an Electrical Engineer for ~35 years).


My best guess is that there were two problems happening concurrently.


1) Someone (hopefully not Nordic Tug) wired the neutral together with the ground on your boat. This is the most common mistake made by 'land-based' electricians. It's done all the time in residential installations, but must !!NEVER!! be done on a boat.
2) At the marina, someone reversed the polarity to the outlet you plugged into.


When you plugged in your cable, the 'hot' line was coming into the boat on the neutral wire. The neutral (which is now 'hot'') was connected on your boat to the ground wire, hence the short. The reason that your breaker didn't blow on the boat is (again, guessing here) because the illegal neutral-to-ground connection was made >>before<< getting to your main breaker. I am assuming that Nordic Tug would be using double-pole breakers (as they should have been in 2008).


This is the only scenario I can imagine that fits the evidence you provided.


Bottom line...NEVER let a land-based electrician touch any wiring on a boat.

 

[Riverguy]

Our 'new to us' boat has 50A 120 service also. But noticed the shore cord had a 50A 240 plug on the shore end, and a 50A 120 plug on the boat end - a big no-no. Changed shore end to 50A 125 (discovered old plug wires were corroded and breaking apart), and bought an expensive adapter for 50A 120 to 50A 240 for marina's that don't have 50A 120. Feel much safer now

Actually, you can safely wire up a shore-power cable with NEMA SS-2 plug (aka 50A 125/250) to a NEMA SS-1 receptacle (aka 50A-125V). It is perfectly legit and perfectly safe, because you are only using one "leg" of the SS-2 (50A-125/250V) service, in this case L1. In fact, if you were to look inside the adapter you bought, you'd find the SS-2 plug is wired neutral-neutral (white-to-white), with L1 to 'hot' and L2 not connected. So...a 50A cable with an SS-2 plug at one end and an SS-1 receptacle at the other end is then just a really long 'adapter'.

 

[Riverguy]

Mystery solved?

I'm late to the thread, but I have recently completed ABYC E-11 training (on top of that I have worked as an Electrical Engineer for ~35 years).


My best guess is that there were two problems happening concurrently.


1) Someone (hopefully not Nordic Tug) wired the neutral together with the ground on your boat. This is the most common mistake made by 'land-based' electricians. It's done all the time in residential installations, but must !!NEVER!! be done on a boat.
2) At the marina, someone reversed the polarity to the outlet you plugged into.


When you plugged in your cable, the 'hot' line was coming into the boat on the neutral wire. The neutral (which is now 'hot'') was connected on your boat to the ground wire, hence the short. The reason that your breaker didn't blow on the boat is (again, guessing here) because the illegal neutral-to-ground connection was made >>before<< getting to your main breaker. I am assuming that Nordic Tug would be using double-pole breakers (as they should have been in 2008).


This is the only scenario I can imagine that fits the evidence you provided.


Bottom line...NEVER let a land-based electrician touch any wiring on a boat.

I just noticed from your photos...it appears that you had 2x 30A cables connected to the pedestal. This resolves the last piece of the puzzle -- it explains why only the one ground wire got fried. Essentially, you had 2x 30A = 60A returning through the ground wire of the miswired outlet.



Bottom line, it took two to do this Short Circuit tango:


1) Boat miswired: Someone combined the neutral with the ground aboard your boat and/or combined the neutrals from each of the two inlets aboard the boat. Either of these is strictly verboten.


2) Marina: the pedestal was most definitely wired wrong.


This is >>exactly<< the scenario that the ABYC E-11 rules are intended to prevent.


It is very lucky that you discovered the problem before it started a fire aboard your boat!

 

[CMS]

Just saw this and it looks like Riverguy is on the mark. I will only add that inadvertent neutral/ground bonds on-board the boat are most often created by boat owners themselves and then unqualified electricians. Builders, at least most of them, have understood this for many, many years.

If I had a dime for every inverter installation I’ve seen where a permanent neutral/ground bond was made I’d be a lot closer to retirement.

The only time neutral and ground are allowed to be bonded on-board are when you are unplugged from shore power and actively inverting or actively using a genset. These bonds need to be broken when those units are no longer operating. The secondary side of an isolation transformer would also be an exception as it is now your "source" of AC power.

Also any time you have two shore power services on-board they two can not be commingled and must remain separate other than for AC grounding.

I see two AC inlets/systems sharing a neutral bus all too often.

 

[Boat]

Out of phase? If the two 110V supplies are out of phase, they add together and make a 220V supply to fry your boat. L1 to L2? You can use two 110V cords to supply 110V or you can use two 110V cords to supply 220V.


Or was it one cord?

I have no idea if that is what happened but when you use two 110s in parallel you have to be acutely aware of this possibility. Maybe some boats are protected? Protection at the pedestal?

If it is something different about that pedestal, maybe it is wired out of phase. Or in other words, L1 on one, L2 on the other.

What a can of worms. Then it starts getting complicated. Delta, Wye, L1, L2, ground, earth, centertap. Is it real or is it a wordgame?


Earlier in the thread people were advocating involving insurance. Use it and lose it seems to be a rule with some insurance these days. Is this a concern?

 

[bglad]

It will be interesting to hear the diagnosis from the OP if willing to share. I agree with Riverguy that it sure seems to be a pedestal problem unless there is an inverter involved then it could be complicit. The trail of melted wiring should offer more evidence about what happened.

 

[FoxtrotCharlie]

Actually, you can safely wire up a shore-power cable with NEMA SS-2 plug (aka 50A 125/250) to a NEMA SS-1 receptacle (aka 50A-125V). It is perfectly legit and perfectly safe, because you are only using one "leg" of the SS-2 (50A-125/250V) service, in this case L1. In fact, if you were to look inside the adapter you bought, you'd find the SS-2 plug is wired neutral-neutral (white-to-white), with L1 to 'hot' and L2 not connected. So...a 50A cable with an SS-2 plug at one end and an SS-1 receptacle at the other end is then just a really long 'adapter'.

While I'm not a electrician either, the guy working on our boat was a licensed marine electrician - and he said he would not be allowed to put back the 50A 250 shore end (the bad one we discovered), with a 50A 125 on the boat end - said not allowed by code .....hence the adapter. I thought it would work ok, but I can see the issue of confusion.